Compound spring arrangement for brush holders of rotary electric machines

ABSTRACT

Spring arrangement for the brush holders of a rotary electric machine. The spring arrangement is made by combining two kinds of springs, that is, a conventional spiral spring and a V-shaped leaf spring, in such a manner that the deflection angle of the Vshaped leaf spring opposes the deflection angle of the spiral spring so that the horizontal component of the pressing force of the spiral spring on the brush is cancelled by the horizontal component of the pressing force of the V-shaped leaf spring on the brush for all positions of the brush.

United States Patent [191 Nakamura et al.

[ 1 COMPOUND SPRING ARRANGEMENT FOR BRUSH HOLDERS OF ROTARY ELECTRIC MACHINES [75] Inventors: Toshio Nakamura; Yasuzi Sakuma;

Hitoshi Egawa; Sadaharu Kawai; Shoji Motegi, all of Hitachi, Japan [73] Assignee: Hitachi, Ltd., Tokyo, Japan [22] Filed: Oct. 7, 1971 [2]] App]. No.: 187,279

[30] Foreign Application Priority Data Oct. 7, 1970 Japan 45-87553 [52] US. Cl. 310/246 [51] Int. Cl. H02k 13/00 [58] Field of Search 310/245, 242, 246, 247, 310/244, 239

[56] References Cited UNITED STATES PATENTS 1,396,451 11/1921 Merk 310/246 [111 3,816,783 June 11, 1974 2,488,788 1 1/1949 Weilbaecher 310/246 2,964,663 12/1960 Jowett 310/246 3,025,422 3/1962 Rusynyk 310/246 3,146,365 8/1964 Millar 310/246 3,590,298 6/1971 Hudak 310/246 Primary Examiner-R. Skudy Attorney, Agent, or Firm-Craig and Antonelli 5 7] ABSTRACT Spring arrangement for the brush holders of a rotary electric machine. The spring arrangement is made by combining two kinds of springs, that is, a conventional spiral spring and a V-shaped leaf spring, in such a manner that the deflection angle of the V-shaped leaf spring opposes the deflection angle of the spiral spring so that the horizontal component of the pressing force of the spiral spring on the brush is cancelled by the horizontal component of the pressing force of the V- shaped leaf spring on the brush for all positions of the brush.

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ATT RN EYS COMPOUND SPRING ARRANGEMENT FOR BRUSH HOLDERS OF ROTARY ELECTRIC MACHINES BACKGROUND OF THE INVENTION This invention relates to brush holders for rotary electric machines which form part of the current collectors, i.e., along with the commutator and collecting ring, of the machine, and more particularly to the spring means for the brush holders thereof.

In the brush holders of an electric motor for an electric locomotive, spiral springs are generally employed to press the brush firmly onto the surface of the commutator. This mechanism which produces a pressing of the brush by the spiral springs is quite simple and light in weight. In addition, the standard mechanism provides a good association between the commutator and the brush and also has good vibration proof characteristics. As a result, this mechanism is widely employed as a brush holder structure in electric motors for electric locomotives, wherein they usually are subjected to the most severe conditions.

Recently, it has been necessary to increase the speed of the electric locomotive and to make the components thereof more maintenance free. To meet these requirements, attempts have been made to prolong the inspection intervals and the exchange time of the brush by making it physically longer and by decreasing the wear to which it is subjected.

FIG. 1 is a prior art brush pressing mechanism of the type described above. Numeral l is a spiral spring made of thin leaf spring material, the inner end of the spiral spring being fixed to a fixed axial member 3. On the outer or free end of the spiral spring a plate member 2 is attached, through which the stored pressing energy of the spring is exerted on a brush 4. The plate member 2 is rotatable around the fixed axial member 3 and so the direction of the spring pressure exerted through the plate member on one end of the brush is tangential to the rotating route or locus of the plate member. Accordingly, at an early stage in the use of the brushthe tangential force F, is directed to the left, as seen in FIG. 1, with respect to the vertical direction of movement of the brush. The tangential force F, therefore comprises a horizontal component Ph so that the vertical component Pv actually urging the brush toward the rotating commutator is smaller than the tangential force P When the brush 4 moves to the position shown as 4a in FIG. 1 due to the progressive wear thereof, the tangential direction of the pressure of the plate member 2 coincides with the longitudinal axial direction of the brush, that is, the vertical direction, so that the tangential force P itself is the same as that of the vertical force Pv, and all of the stored energy of the spring can be utilized for pressing upon the brushes.

When the brush 4 further moves to the position shown as 4b in FIG. 1, the tangential force P is directed to the right with respect to the vertical direction. The tangential force P comprises a horizontal component Ph so that the vertical component Pv actually urging the brush toward the rotating conductor is again smaller than the tangential force P FIG. 2 shows the relationship between the deflection angle from a standard point and the tangential force for explaining the pressing force of the spring in FIG. ll. As seen from FIG. 2, the tangential forces P P and P are proportional to the deflection angles 8 8 and 6 respectively, as shown by the straight line K However, the vertical force component acting on the brush 4 is Pv, Pv and Pv when the deflection angles are 8 8 and 8 respectively, and the relationship between the deflection angle and the vertical component is represented by the curved line Kv.

As will be understood from the above explanation, the vertical force component acting on the brush changes to a large extent in accordance with the height of the brush. Consequently, it is necessary to set the vertical force during the early stage of use high so that it will not become extremely low at the final stage of use of the brush, that is when the limited wearing point of the brush is reached. When the vertical force on the brush becomes lower than a certain minimum level, it

becomes difficult to hold the brush in place, and the brush jumps on the rotating commutator to cause an insufficient current collection and commutation and finally to reduce the electric characteristics of the rotary electric machine. Further, when the brush 4 jumps, sparks occur between the brush and the conductors, and the brush 4 wears at an abnormally high rate. In addition, if the vertical force during the early stage of use of the brush has been set high, the brush wears extremely fast for obvious mechanical reasons.

When the variation of the vertical force is large, the brush wears in a relatively short period, that is, the durability of the brush decreases, and it is difficult to meet the maintenance free requirements of the brush holder. Since the maximum horizontal component sometimes reaches 30-40 percent of the tangential component, the brush 4 is forced onto the side wall of the brush holding frame (not shown) and inclines with respect to the vertical line. Due to this inclination, an abnormal wearing of the brush may occur, and the brush will not sit on the conductor positively. Thus, the good association between the brush and the conductor is decreased. Finally, the electric characteristics of the rotary electric machine are reduced because of these defects in the brush and its holder.

To overcome these drawbacks, it has been proposed to reduce the degree of inclination of the brush by making the brush longer; however, with this construction, the horizontal component becomes extremely large to the point where it may exceed the vertical component. As a result, the brush 4 is heavily forced onto the side wall of the brush holding frame, and good sliding contact between the brush and the commutator is impossible to achieve.

Further, as the rotational speed of the rotary electric machine increases, the range of the vibration frequency applied to the brush becomes larger, with the result that the brush holder assembly with the abovedescribed simple spiral spring construction is likely to vibrate in resonance with a frequency within the expanded range.

SUMMARY OF THE INVENTION Accordingly, one object of the present invention is to provide a spiral spring structure for the brush holder of a rotary electric machine which provides improved current collecting and commutating characteristics.

Another object of the invention is to provide a spiral spring structure for the brush holder of a rotary electric machine which is particularly suitable for use at high rotational speeds.

Another object of the invention is to provide a spiral spring for the brush holder of a rotary electric machine which prolongs the maintenance interval of the brush holder.

Briefly stated, the present invention provides a second V-shaped leaf spring at the free end of the spiral spring of the brush holder in such a manner that the deflection angle of the V-shaped leaf spring complements that of the spiral spring. As a result, the horizontal component of the spiral spring is eliminated; in other words, the pressing force exerted on the brush by the combined spring means consists of only a vertical component.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary side view of a known brush holder construction;

FIG. 2 is a graph showing the relationship between the deflection angle from a standard point and the tangential force of the spiral spring of FIG. 1;

FIG. 3 is a schematic diagram of a combination pressing spring for the brush holder of the present invention;

FIG. 4 is a fragmentary side view of the brush holder of the present invention with the brush shown under pressure;

FIG. 5 is a graph showing the relationship between the deflection angle from a standard point and the tangential force of the combination spring means of FIG. 3 and FIG. 4;

FIG. 6 is a side view of a modified combination spring means of the present invention;

FIG. 7 is a side view of another modified combination spring means of the present invention; and

FIG. 8 is a perspective view of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIGS. 3 and 4, a spiral spring 10 is formed by coiling a long thin leaf spring. The inner end of the spiral spring 10 is fixed to the fixed axial member 30, and on an outer or free end of the spiral spring 10, a V-shaped leaf spring 50 is attached in such a manner that the deflection angle 8a of the spiral spring 10 opposes the deflection angle 5b of the V-shaped second leaf spring. In FIG. 4, the V-shaped leaf spring 50 is made of only one sheet-like spring; however, the V-shaped leaf spring can be made by laminating a plurality of sheet-like springs.

Numeral is a plate member which transfers the stored energy of the combination spring to the brush 40. The plate member 20 is attached to the free end of the V-shaped leaf spring. Numeral 50a depicts a stopper which extends perpendicularly from the fixed end of the V-shaped leaf spring 50, and the end of the stopper'50a is bent so as to engage an extending portion 50b of the other end portion or free end of the V- shaped leaf spring 50.

The combination spring means of the brush holder is constructed as described in connection with FIG. 4. At the early stage of use of the brush v40, the tangential pressing force of the spiral spring 10 is directed downward to the left, as seen in the drawing, however the tangential pressing force of the V-shaped leaf spring 50 is directed downward to the right so that the horizontal components of the respective tangential forces cancel each other, and the pressing force acting on the brush 40 corresponds only to the vertical component.

The direction of both tangential forces changes mutually at a predetermined position. Through all positions of the brush 40, the horizontal component does not appear at all by the combination spring mechanism of the present invention. Accordingly, in every position of the brush, the pressing force exerted on the brush is always vertical and the plate member 20 is always maintained in a horizontal position.

If the spring constants of the spiral spring 10 and the V-shaped leaf spring are Ka and Kb, respectively, as shown in FIG. 5, then the spring constant of the resultant combination spring, that is, the spring constant of serially connected spring arrangement, is represented by the following equation.

K10 F o/81o In the above equation, 8a is the deflection angle of the spiral spring 10 during its original stage of use, 612 is the deflection angle of the V-shaped leaf spring 50 during its original state of use, 8 is a summation of 5a and 8b and represents the deflection angle of the combined spring formed by the spiral spring 10 and the leaf spring 50 in its original position, and P represents the pressing force of the combined spring on the brush 40 in its original position.

The spring constant of the combined spring, which is formed by connecting the two springs together, becomes smaller than the spiral spring alone, and the variation of the pressing force on the brush 40 is reduced, as seen by P P and P with respect to the deflection angle 6 8 and 6 respectively, in FIG. 5. As the height of the brush decreases, the pressing force of the combined spring on the brush decreases. In other words, a favorable pressing force characteristic responsive to the mass of the brush can be obtained. As a result, the wear on the brush caused by mechanical and electrical factors is limited to a minimum.

Further, since the horizontal component of the spiral spring and the V-shaped spring cancel each other and the plate member 20 is kept substantially horizontal for all positions of the brush, the brush can sit on the commutator firmly and also the association between the brush and the conductor is improved. Consequently, the current collecting and commutating characteristics of the rotary electric machine are improved.

In addition, as the plate member 20 is kept substantially in a horizontal position at all times, the height of the brush can be increased; as the result, the exchanging interval of the brush can be prolonged.

Further, the resonance frequency of the combined spring can be controlled by adjusting the frequency of either of the two individual springs. As a result, resonance of the combined spring is effectively prevented even for high speed operation of the rotary electric machine in which the resonant frequency of the machine varies over a wide range.

Furthermore, as the plate member 2 of the conventional spiral spring shown in FIG. 1 inclines in accordance with the position of the brush and the pressing point of the plate member 2 upon the brush varies, the height of the square edge brush shown in FIG. 6 is limited, and even with the round edge brush shown in FIGS. 1 and 4, they cannot sit on the conductor firmly if the height of them is increased. On the other hand, with the combined spring of the present invention, the

plate member is kept in a horizontal orientation for all positions of the brush so that the edge shape of the brush need not be limited. Any edge shape can be chosen in accordance with the situation.

As the stopper 50a and the engaging member 50b are arranged on respective end portions of the V-shaped leaf spring to limit the deflection angle thereof within a predetermined amount, the insertion and extraction of the brush 40 from the brush holding frame can be accomplished easily without any trouble and the plate member 20 can be disposed easily and conveniently on a predetermined end portion of the brush.

In the above description, only the V-shaped leaf spring is described as the second spring means which is attached on the outer or free end of the spiral spring. However, the second spring means can also be a combination of two coil springs 500, as shown in FIGS. 7 and 8, wherein plate member 200 is provided on which each one end portion of the both coil spring is attached. The plate member 200 also serves as an engaging member 50Gb which engages with a stopper 500a extending from each of the other end portions of the coil springs.

We claim:

1. A spring arrangement for the brush holders of a rotary electric machine, comprising a brush disposed for sliding movement in a given direction,

a spiral spring, the inner end of which is fixed to a fixed member and the outer end of which is bent in the form of a radial extension,

additional spring means secured to the radial extension of said spiral spring for providing an independent component of force at the radial extension of said spiral spring which is transverse to the path of movement of said brush and equal and opposite to the corresponding transverse force provided by said spiral spring so as to substantially cancel all forces on said brush which are transverse to the path of movement thereof for all positions of said brush, and

a plate member secured to said additional spring means and contacting said brush.

2. A spring arrangement as defined in claim 1, wherein said additional spring means includes a V- shaped spring having one leg secured to said radial extension of said spiral spring and the other leg secured to said plate member.

3. A spring arrangement as defined in claim 2 wherein said additional spring means further includes stopper means extending from one end of said V- shaped spring for engaging with the other end of said V-shaped spring upon opening of said spring to a predetermined extent to restrict the degree of opening thereof.

4. A spring arrangement for the brush holders of a rotary electric machine, comprising a brush disposed for sliding movement in a given direction,

a spiral spring, the inner end of which is fixed to a fixed member and the outer end of which is bent in the form of a radial extension,

additional spring means secured to the radial extension of said spiral spring for providing an independent component of force substantially canceling all forces at said radial extension which are transverse to the path of movement of said brush for all positions thereof, and

a plate member secured to said additional spring means and contacting said brush so as to apply a force thereto from the combination of said spiral spring and said additional spring means which is essentially only in line with the path of movement of said brush.

5. A spring arrangement as defined in claim 4, wherein said additional spring means includes an additional spring and stopper means for restricting the length of effective movement of said additional spring.

6. A spring arrangement as defined in claim 4, wherein said additional spring means includes a V- shaped spring having one leg secured to said radial extension of said spiral spring and the other leg secured to said plate member.

7. A spring arrangement as defined in claim 4, wherein said additional spring means includes a combination spring formed by two coil springs, one end of each coil spring being attached to said radial extension of said spiral spring and the other end of each coil spring being attached to said plate member.

8. A spring arrangement as defined in claim 7, wherein said additional spring means further includes stopper means for restricting the degree of opening of said two coil springs. 

1. A spring arrangement for the brush holders of a rotary electric machine, comprising a brush disposed for sliding movement in a given direction, a spiral spring, the inner end of which is fixed to a fixed member and the outer end of which is bent in the form of a radial extension, additional spring means secured to the radial extension of said spiral spring for providing an independent component of force at the radial extension of said spiral spring which is transverse to the path of movement of said brush and equal and opposite to the corresponding transverse force provided by said spiral spring so as to substantially cancel all forces on said brush which are transverse to the path of movement thereof for all positions of said brush, and a plate member secured to said additional spring means and contacting said brush.
 2. A spring arrangement as defined in claim 1, wherein said additional spring means includes a V-shaped spring having one leg secured to said radial extension of said spiral spring and the other leg secured to said plate member.
 3. A spring arrangement as defined in claim 2 wherein said additional spring means further includes stopper means extending from one end of said V-shaped spring for engaging with the other end of said V-shaped spring upon opening of said spring to a predetermined extent to restrict the degree of opening thereof.
 4. A spring arrangement for the brush holders of a rotary electric machine, comprising a brush disposed for sliding movement in a given direction, a spiral spring, the inner end of which is fixed to a fixed member and the outer end of which is bent in the form of a radial extension, additional spring means secured to the radial extension of said spiral spring for providing an independent component of force substantially canceling all forces at said radial extension which are transverse to the path of movement of said brush for all positions thereof, and a plate member secured to said additional spring means and contacting said brush so as to apply a force thereto from the combination of said spiral spring and said additional spring means which is essentially only in line with the path of movement of said brush.
 5. A spring arrangement as defined in claim 4, wherein said additional spring means includes an additional spring and stopper means for restricting the length of effective movement of said additional spring.
 6. A spring arrangement as defined in claim 4, wherein said additional spring means includes a V-shaped spring having one leg secured to said radial extension of said spiral spring and the other leg secured to said plate member.
 7. A spring arrangement as defined in claim 4, wherein said additional spring means includes a combination spring formed by two coil springs, one end of each coil spring being attached to said radial extension of said spiral spring and the other end of each coil spring being attached to said plate member.
 8. A spring arrangement as defined in claim 7, wherein said additional spring means further includes stopper means for restricting the degree of opening of said two coil springs. 